Likely caused by pollution, levels of mercury in the fish have been on the rise steadily since 1998. You can limit your exposure by following FDA guidelines for fish consumption.

There's a lot more mercury in this yellowfin tuna than there was a couple of decades ago.
(Photo: Paul Binet/Shutterstock)

Studies have already shown that 84 percent of the world’s fish have unsafe levels of mercury. Now, a new scientific study published in the journal Environmental Toxicology and Chemistry says those levels are rising, at least in Pacific yellowfin tuna. The LA Times reports the level of mercury in yellowfin caught in the Pacific Ocean has risen at a rate of 3.8 percent a year since 1998.

At the moment, the level of mercury in the fish is “not likely to be a health hazard.” Researchers believe the fish are still safe to eat, but if the mercury levels continue to rise at this rate, that may not hold true for the future.

Carl Lamborg, one of the authors of the study, says, “The amount of mercury in fish is getting higher and higher all the time, and if it keeps going like that, at some point, most every kind of fish is going to be potentially hazardous." When that point is, he doesn’t know.

Causes of mercury in fish

According to this new study, evidence points to air pollution as a cause for the rise in methylmercury, the type of mercury found in fish. Mercury emissions from burning coal in particular fall into the ocean, contaminating fish and shellfish.

Effects of mercury in fish on health

The Environmental Protection Agency says most Americans “are mainly exposed to methylmercury, an organic compound, when they eat fish and shellfish that contain methylmercury.” The compound may be organic, but it can also cause a variety of health problems, including impaired numerological development in fetuses, infants and children.

Other symptoms of methylmercury poisoning include “impairment of the peripheral vision; disturbances in sensations (that "pins and needles" feeling, usually in the hands, feet, and around the mouth); lack of coordination of movements; impairment of speech, hearing, walking; and muscle weakness.”

Limiting exposure of mercury through fish

The FDA released advice for women who are planning to become pregnant, are pregnant or are breastfeeding, and also for anyone who feeds young children. These are the populations most at risk from exposure to methylmercury. However, anyone who wants to limit exposure to mercury from fish can follow the FDA's guide: Fish: What Pregnant Women and Parents Should Know.

Adults should have eight to 12 ounces of a variety of fish that are low in mercury. Salmon, shrimp, pollock, tuna (light canned), tilapia, catfish, and cod are recommended.

Young children should have two to three servings of these fish per week at the proportion that is right for them.

Avoid tilefish from the Gulf of Mexico, shark, swordfish and king mackerel. They contain the highest amount of mercury.